Traverse Hardening Device and Traverse Hardening Method

The present disclosure relates to a traverse hardening device and a traverse hardening method.

Conventionally, traverse hardening is performed on a shaft-like body by induction heating to increase fatigue strength of the shaft-like body. The term “traverse hardening” as used herein means that hardening is performed while a coil member or the like is moved in an axial direction with respect to a shaft-like body.

Specifically, a shaft-like body is induction-heated by causing a current to flow through a coil while the coil is moved along an outer circumferential surface in a longitudinal direction of the shaft-like body. Then, the shaft-like body is rapidly cooled and hardened by spraying a coolant to the outer circumferential surface immediately after heating. Here, when the shaft-like body is a stepped shaft having a level difference portion in which an outer diameter changes from a large diameter to a small diameter or from a small diameter to a large diameter at an intermediate position in a longitudinal direction thereof, it is necessary to appropriately adjust an air gap between the outer circumferential surface of the shaft-like body and the coil in order to maintain heating efficiency.

As one of device configurations that enable such adjustment, there is a mode in which the coil is constituted by a plurality of divided coils. Specifically, the plurality of divided coils are arranged in a circumferential direction of the shaft-like body, and these divided coils are connected in series to a power source. Then, these divided coils are moved in a longitudinal direction of the shaft-like body while a current from the power source flows through the divided coils. Then, immediately before the divided coils reach a level difference portion, the divided coils are brought close to or away from an outer circumferential surface of the shaft-like body depending on a change in the outer diameter dimension of the shaft-like body, whereby the air gap is maintained substantially constant.

A conventional high-frequency induction heating device using this type of divided coil is disclosed in Patent Document 1 below. The device includes a high-frequency induction heating coil as the divided coil. This high-frequency induction heating coil adopts a configuration of “a shaft-shaped member heating high-frequency induction heating coil for performing high-frequency induction heating, in a shaft-shaped member having a flange section and a shaft portion erected at a central portion of the flange section, an arc portion formed between the flange section and the shaft portion intersecting with each other and a outer circumferential surface of the shaft portion, the high-frequency induction heating coil including a pair of high-frequency induction heating coil components disposed at positions facing each other across an axis of the shaft-shaped member and disposed facing the arc portion and the shaft portion at a position spaced apart from the arc portion and the shaft portion of the shaft-shaped member, in which a bent coil portion bent so as to protrude in a direction away from the axis of the shaft-shaped member is formed in each of the pair of high-frequency induction heating coil components”.

There is description that, according to the device, “by using the pair of high-frequency induction heating coil components, the pair of high-frequency induction heating coil components described above can be disposed correspondingly to all of various shaft-shaped members having different diameters of outer circumferential surfaces”.

By the way, in a conventional traverse hardening device including the above device, the number of windings of the divided coil is one, and the number of windings cannot be increased to two or more due to structural reasons. This is because when the number of windings is increased by overlapping a plurality divided coils along a longitudinal direction of a shaft-like body, traverse hardening cannot appropriately performed on a level difference portion where an outer diameter of the shaft-like body changes. For example, in traverse hardening of a level difference portion from a large diameter portion toward a small diameter portion, the divided coils cannot be brought close to the small diameter portion until the entire divided coils overlapping with each other in the longitudinal direction of the shaft-like body pass the large diameter portion. Therefore, a portion of the divided coils on a front side in a traveling direction, which has reached the small diameter portion after finishing heating of the large diameter portion, performs induction heating while having a wide air gap with an outer circumferential surface of the small diameter portion, which is not preferable from a viewpoint of heating efficiency and irregular hardening pattern.

On the other hand, in traverse hardening of a level difference portion from the small diameter portion toward the large diameter portion, even in the middle of heating the small diameter portion, a portion on a rear side in a traveling direction in the divided coils overlapping with each other in the longitudinal direction of the shaft-like body cannot get over the level difference portion unless the portion on the rear side is moved away early from the outer circumferential surface of the small diameter portion at a point of time before a portion on the front side in the traveling direction reaches the large diameter portion. Therefore, the result is also not preferable from a viewpoint of heating efficiency and irregular hardening pattern.

For the reasons described above, the number of windings of the divided coil up to now cannot be two or more, and one winding is normal. In the case of one winding, it is necessary to set a current flowing through the divided coil to an extremely high current as compared with a case of a plurality of windings, and thus problems such as overheating and short circuit of the divided coil are likely to occur.

The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide a traverse hardening device and a traverse hardening method capable of performing traverse hardening on a stepped shaft while suppressing overheating and short circuit of a divided coil due to a large current.

In order to solve the problem described above, the present disclosure proposes the following aspects.

(1) A traverse hardening device according to an aspect of the present disclosure performs traverse hardening on a shaft-like body in which a large diameter portion having a relatively large outer diameter and a small diameter portion having a relatively small outer diameter are connected via a level difference portion, the device including:

According to the traverse hardening device described in the above (1), a high-frequency current flows through the first divided coils and the second divided coils while moving the first divided coils and the second divided coils in a state where the first divided coils and the second divided coils are arranged around the shaft-like body and overlap each other in a direction along the motion center line. Then, electromagnetic induction occurs between the first divided coils/second divided coils and the shaft-like body, and the shaft-like body is induction-heated.

When the shaft-like body is induction-heated while the first divided coils and the second divided coils are moved in this manner, in a case where the first divided coils induction-heat the level difference portion while the second divided coils induction-heat the small diameter portion, the control unit drives the first divided coil drive unit to gradually move the positions of the first divided coils outward in a radial direction of the shaft-like body. By this movement, the first divided coils can be moved along an outer circumferential surface without interfering with the level difference portion while the second divided coils are kept along a periphery of the small diameter portion.

Furthermore, when the second divided coils induction-heat the level difference portion, and at the same time, the first divided coils induction-heat the large diameter portion, the control unit drives the second divided coil drive unit to gradually move the positions of the second divided coils outward in a radial direction of the shaft-like body. As a result, the second divided coils can be moved along an outer circumferential surface of the level difference portion without interfering with the level difference portion while the first divided coils are kept along a periphery of the large diameter portion.

On the other hand, when the small diameter portion is induction-heated from the large diameter portion beyond the level difference portion, contrary to the above procedure, the first divided coil drive unit brings the first divided coils close to an outer circumferential surface of the shaft-like body, and the second divided coil drive unit brings the second divided coils close to the outer circumferential surface of the shaft-like body. The approach operations of the first divided coils and the second divided coils to the shaft-like body are individually performed depending on outer diameters of portions to be induction-heated by the first divided coils and the second divided coils.

Therefore, it is possible to solve the problem of interference with the shaft-like body that occurs when the first divided coils and the second divided coils overlap each other in the direction of the motion center line. As a result, since traverse hardening can be performed by a two or more-winding divided coil (the first divided coil and the second divided coil), a current value of a high-frequency current flowing through each of the divided coils can be significantly reduced as compared with that of a one-winding coil.

Note that the coil that heats the shaft-like body is not limited to the two coils of the first divided coil and the second divided coil. Three or more divided coils may be overlapped in the direction of the motion center line. In this case, it is preferable to adopt three or more divided coil drive units as many as the divided coils.

(2) In the traverse hardening device described in the above (1), the following configuration may be adopted:

According to the traverse hardening device described in the above (2), since the control unit individually controls a current value in the first divided coils and a current value in the second divided coils, the current value can be adjusted to a current value suitable for a heating portion of the shaft-like body. For example, when a corner portion formed at a connection portion between the level difference portion and the large diameter portion is heated by the first divided coils, by increasing a current value in the first divided coils, the corner portion can be sufficiently heated without reducing a moving speed of the first divided coils.

Note that, as a method for heating the corner portion to a higher temperature, it is also conceivable to reduce the moving speed when the first divided coils pass the corner portion. However, in this case, it is necessary to reduce a moving speed of the cooling ring that cools the shaft-like body after heating. Therefore, the moving speed of the cooling ring cannot be made constant in an axial direction, and uneven cooling occurs. On the other hand, in the present aspect, since it is not necessary to reduce the moving speed, there is an advantage that such a trouble does not occur.

(3) In the traverse hardening device described in the above (2), the following configuration may be adopted:

According to the traverse hardening device described in the above (3), the control unit controls the variable resistor, whereby a current value of a high-frequency current flowing through the first divided coils and a current value of a high-frequency current flowing through the second divided coils can be adjusted to either different values or the same value. Therefore, a high-frequency current corresponding to a heating portion of the shaft-like body can be set for each of the first divided coils and the second divided coils.

(4) A traverse hardening method according to an aspect of the present disclosure is for performing traverse hardening on a shaft-like body in which a large diameter portion having a relatively large outer diameter and a small diameter portion having a relatively small outer diameter are connected via a level difference portion, the method including:

According to the traverse hardening method described in the above (4), it is possible to obtain the same effect as the effect of the traverse hardening device described in the above (1). Therefore, it is possible to solve the problem of interference with the shaft-like body that occurs when the first divided coils and the second divided coils overlap each other in the direction of the motion center line. As a result, since traverse hardening can be performed by a two or more-winding divided coil (the first divided coil and the second divided coil), a current value of a high-frequency current flowing through each of the divided coils can be significantly reduced as compared with that of a one-winding coil.

(5) In the traverse hardening method described in the above (4), a current value of a high-frequency current flowing through the first divided coils and a current value of a high-frequency current flowing through the second divided coils may be individually controlled during the traverse hardening.

According to the traverse hardening method described in the above (5), it is possible to obtain the same effect as the effect of the traverse hardening device described in the above (2). Therefore, since traverse hardening can be performed while the moving speeds of the first divided coils and the second divided coils are kept constant, uneven cooling can be suppressed while a moving speed of the cooling ring following the first divided coils and the second divided coils is also kept constant.

According to the traverse hardening device and the traverse hardening method according to the aspects described above, it is possible to perform traverse hardening on the stepped shaft while suppressing overheating and short circuit of the divided coil due to a large current.

Hereinafter, an embodiment of a traverse hardening device and a traverse hardening method according to the present disclosure will be described with reference to the drawings. In the following description, a direction along a central axis CL of a shaft-like body W may be referred to as a longitudinal direction, a radial direction of the shaft-like body W around the central axis CL may be simply referred to as a radial direction, and a circumferential direction of the shaft-like body W may be referred to as a circumferential direction. A motion center line which is a center line of the first divided coils and the second divided coils is used in order to indicate a direction in which the first divided coils and the second divided coils included in the traverse hardening device are moved. The motion center line is a straight line coinciding with the central axis CL. In, an upper side of the drawing along the motion center line may be simply referred to as an upper side, and a lower side of the drawing may be simply referred to as a lower side.

First, a configuration of a traverse hardening device according to the present embodiment will be described with reference to. Here,is a side view schematically illustrating a part of the traverse hardening device in a broken state.is a view of a pair of first divided coils included in the traverse hardening device as viewed from above, and is a view taken in a direction of an arrow A-A in.is a circuit diagram schematically illustrating electrical connection between a high-frequency power source and the first divided coil/second divided coil.

A traverse hardening deviceillustrated inis a device that performs traverse hardening on a railway vehicle axle or a shaft-like body W such as a ball screw using a high-frequency current.

First, the shaft-like body W will be described. The shaft-like body W is a stepped shaft in which a large diameter portion W, a level difference portion W, a small diameter portion W, a level difference portion W, and a large diameter portion Ware coaxially disposed in this order from a lower side to an upper side in a longitudinal direction thereof. The large diameter portions Wand Ware cylinders having a circular flat cross section, and have the largest outer diameter in the whole shaft-like body W. The small diameter portion Wis a cylinder having a circular flat cross section, and has an outer diameter smaller than those of the large diameter portions Wand W. The level difference portion Whas a truncated cone shape connecting an upper end of the large diameter portion Wand a lower end of the small diameter portion W. An outer diameter of the level difference portion Wgradually decreases from the same outer diameter as the large diameter portion Win an upward direction, and becomes equal to an outer diameter of the lower end of the small diameter portion W. The level difference portion Whas an inverted truncated cone shape connecting an upper end of the small diameter portion Wand a lower end of the large diameter portion W. An outer diameter of the level difference portion Wgradually increases from the same outer diameter as an outer diameter of the upper end of the small diameter portion Win the upward direction, and becomes equal to an outer diameter of the lower end of the large diameter portion W. The large diameter portion W, the level difference portion W, the small diameter portion W, the level difference portion W, and the large diameter portion Wshare the central axis CL. When the outer diameter dimension of each of the large diameter portions Wand Wis 100%, the outer diameter dimension of the small diameter portion Wis, for example, 80% to 90%.

The shaft-like body W is formed of a material having conductivity, such as carbon steel or low alloy steel containing 95% by weight or more of iron (Fe), which includes ferrite phase.

As illustrated in, the traverse hardening device includes a support portion, an induction heating unit, a cooling unit, a moving unit, a control unit, and a power source.

As illustrated in, the support portionincludes a lower centerand an upper center. The lower centercoaxially supports the large diameter portion Wof the shaft-like body W from below. The upper centercoaxially supports the large diameter portion Wof the shaft-like body W from above. The lower centerand the upper centersupport the shaft-like body W such that the central axis CL of the shaft-like body W extends in the vertical direction, one end side (a side where the large diameter portion Wis present) of the shaft-like body W is located on a lower side, and the other end (a side where the large diameter portion Wis present) of the shaft-like body W is located on an upper side. The shaft-like body W is disposed between the lower centerand the upper centerso as to be rotatable about the central axis CL. The lower centerand the upper centerpivotally supporting the shaft-like body W in this manner rotate the shaft-like body W about the central axis CL when receiving a driving force from a shaft-like body rotary motor (not illustrated) included in the support portion.

As illustrated in, the induction heating unitincludes a plurality of coils and a coil support base.

In the present embodiment, two coils of an upper coiland a lower coilare adopted as the plurality of coils. The upper coiland the lower coilhave the same configuration. Therefore, first, the upper coilwill be described below. The lower coilis assumed to be the same as the upper coil, and the same reference numeral is used, whereby redundant description will be omitted. Note that the coil that heats the shaft-like body W is not limited to the two coils of the upper coiland the lower coil. Three or more coils may be overlapped in the direction of the motion center line.

As illustrated in, the upper coilincludes a pair of divided coilsA annularly arranged around the motion center line (central axis CL). Each of the divided coilsA includes a coil main body portiona first conductive wire portionand a second conductive wire portion

The coil main body portionhas an arc shape protruding in the radial direction around the central axis CL. An inner circumferential surface of the coil main body portionis a recessed arc surface around the central axis CL, and is disposed with a constant gap dimension g in a circumferential direction with respect to an outer circumferential surface of the small diameter portion W. The coil main body portioninduction-heats a range of approximately a half circumferential portion (180° portion) in a circumferential direction of the shaft-like body W. Note that, as the shape of the coil main body portioninstead of the arc shape, an L shape or a V shape protruding in a direction away from the central axis CL may be adopted.

The first conductive wire portionis electrically and mechanically connected to one end of the coil main body portionand extends straight substantially outward in the radial direction. The second conductive wire portionis electrically and mechanically connected to the other end of the coil main body portionand extends straight substantially outward in the radial direction. The first conductive wire portionand the second conductive wire portionextend along a common straight line.

The pair of divided coilsA having the above configuration forms one heating coil coaxially disposed around the shaft-like body W by a combination of the two coil main body portionsWhen the small diameter portion Wis induction-heated, by narrowing a relative distance between the pair of divided coilsA, the pair of coil main body portionsis disposed with the gap g around the small diameter portion W.

On the other hand, as illustrated in, when the large diameter portions Wand Ware induction-heated, by expanding the relative distance between the pair of divided coilsA, the pair of coil main body portionsis disposed around the large diameter portions Wand W.

When the level difference portions Wand Ware induction-heated, by expanding or narrowing the relative distance between the pair of divided coilsA depending on a change in the outer diameters of the level difference portions, the pair of coil main body portionsis disposed around the level difference portions Wand W.

Note that when the relative distance between the pair of divided coilsA is adjusted depending on an outer diameter of a heating portion of the shaft-like body W, the gap g is adjusted to be minimized within a range not interfering with the heating portion.

The upper coilhas been described above. In order to give description by distinguishing the divided coilA of the upper coilfrom a divided coil of the lower coil, the following description will be given by imparting a reference numeralA to the divided coil of the lower coil.

As illustrated in, the upper coiland the lower coilare coaxially disposed such that the upper coilis overlapped on the lower coil. That is, the coil main body portionsof the upper coilare coaxially overlapped on the coil main body portionsof the lower coil. Note that, as for a circumferential direction arrangement of the lower coiland the upper coil, the first conductive wire portionand the second conductive wire portionof the lower coilmay overlap the first conductive wire portionand the second conductive wire portionof the upper coilin plane view.

Alternatively, the first conductive wire portionsand the second conductive wire portionsof the lower coildo not have to overlap the first conductive wire portionsand the second conductive wire portionsof the upper coilin plane view. In this case, a gap (non-heating range) formed between the first conductive wire portionsof the lower coiland a gap (non-heating range) formed between the second conductive wire portionscan be covered by heating by the coil main body portionsof the upper coil. Conversely, a gap (non-heating range) formed between the first conductive wire portionsof the upper coiland a gap (non-heating range) formed between the second conductive wire portionscan be covered by heating by the coil main body portionsof the lower coil.

In each of the upper coiland the lower coil, the number of divisions of the coil is two, but is not limited to two, and may be three or more. For example, when the number of divisions is three, an angular range of about 120° in the circumferential direction of the shaft-like body W is heated by one divided coil.

Each of the upper coiland the lower coildescribed above is manufactured by bending, brazing, or the like a hollow pipe having a rectangular cross section, and has conductivity. Each end portion of the first conductive wire portionand the second conductive wire portionis electrically and mechanically connected to a current transformerof the power sourceillustrated in. The current transformercauses a high-frequency current to flow through each of the upper coiland the lower coil.